1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method and, more particularly, to an image processing apparatus and an image processing method which can carry out an image process at a high speed to display a three-dimensional image of a three-dimensional object with reality.
2. Description of the Related Art
In a conventional three-dimensional image processing apparatus, a glow shading or a phone shading described in a reference (ASCII. Vol. 19) is carried out when a three-dimensional image is displayed on a screen. The glow shading is a method of calculating the brightnesses of respective apexes of each of a plurality of polygons to be described later, and linearly interpolating the brightness on the polygon plane based on the calculated values and then determining the brightness of the respective pixels within a three-dimensional image data (hereafter, to be referred to as polygon data). However, this method can not represent a slight change of the brightness in each polygon. A point at which the plurality of polygons are in contact with each other is prominent in a three-dimensional image corresponding to a three-dimensional object having a large curvature. Also, an intensity of a light is mixed on the whole surface of the polygon. As a result, a highlight seems to be unnatural.
The phone shading is a method of considering angles between a polygon having a flat plane and peripheral polygons having flat planes, and then deriving a curved surface in a true state and thereby calculating all brightnesses of the respective pixels within the polygon. Although this method can represent the slight change of the brightness of each pixel within the polygon, a processing speed is slow because of the need of a complex brightness calculation for each pixel. The brightness calculation performed in units of pixels is a process with a heavy load. Thus, it is necessary for the execution of a high speed operation that a plurality of brightness calculation processes are performed in parallel. Hence, the phone shading requires a circuit size larger than a circuit size for the glow shading. For this reason, the phone shading technique can not cope with a television game in which the high speed process is required. Therefore, the glow shading method is usually used in the television game.
Now, the polygon will be described. FIGS. 1A to 1C are schematic diagrams to explain the polygon. At first, an image of an object surface is divided on the basis of a density corresponding to the resolution of an input mapping pattern. At this time, for example, if the resolution of a value representative of a degree of a relative irregularity in respective pixels of the mapping pattern, i.e., a Z value is 4.times.4, the object surface image is divided into 4.times.4 as shown in FIG. 1A. A central point of each of regions obtained by the division is set as an inner apex T, and the coordinates of each inner apex T are shifted in accordance with a value corresponding to the Z value of the mapping pattern. At this time, in a case of a plane surface mapping, the coordinates of the inner apex T are shifted upward and downward in a direction vertical to a flat surface. In a case of a curved surface mapping, the coordinates of the inner apex T are shifted upward and downward in a curved radius direction of a curved surface. Thus, the curved surface is formed as shown in FIG. 1B. This curved surface is divided into a plurality of polygons, especially, to have triangle shapes. As a result, the data of each triangle shape P shown in FIG. 1C is obtained as a polygon data.
By the way, when a design and consideration are carried out by using a computer graphic, it is desired to represent the material feeling of an actual object, namely, to represent the delicate irregular feeling and color on the object surface. Displacement mapping is well known as a method of representing the irregularity on the object surface. However, it is difficult in this method to obtain the information about how the irregularity is to be represented.
A conventional image processing apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-271877). The image processing apparatus disclosed in this reference is an apparatus for giving and displaying desired irregularity, color or pattern to an object surface. The conventional image processing apparatus is composed of a mapping pattern data having a z value. In the image processing apparatus, each pixel is raised or lowered in accordance with the z value so that the irregularity is given to the surface of a three-dimensional image. Also, a mapping section refers to the color of each pixel in the mapping pattern to give the color and/or pattern to the surface of the three-dimensional image. However, the process of giving the irregularity is very complex, so that the number of polygons is excessively increased. As a result, the process speed is decreased.
For example, the image processing apparatus disclosed in the above mentioned reference is realized to use the glow shading. In this case, a displacement mapping process of giving an irregularity to the object surface image and a process of calculating the brightnesses of polygons increased through by the above mentioned process must be executed, so that the load becomes heavier. In order to attain the high speed operation, it is necessary to execute the plurality of displacement mapping processes and the plurality of brightness calculating processes in parallel, as mentioned above. This results in extreme increase of the circuit size as compared with the glow shading.
For example, in a three-dimensional image process used in the television game, it is necessary that an object is operated or moved in real time with reality without uneasiness, in response to information inputted by a key operation of an operator. However, the conventional image processing apparatus has been used only in a range of a static image in which the processing speed is not relatively important, similarly to the glow shading method and the phone shading method.